Climate Change and Eutrophication: A Short Review

Water resources are vital not only for human beings but essentially all ecosystems. Human health is at risk if clean drinking water becomes contaminated. Water is also essential for agriculture, manufacturing, energy production and other diverse uses. Therefore, a changing climate and its potential effects put more pressure on water resources. Climate change may cause increased water demand as a result of rising temperatures and evaporation while decreasing water availability. On the other hand, extreme events as a result of climate change can increase surface runoff and flooding, deteriorating water quality as well. One effect is water eutrophication, which occurs when high concentrations of nutrients, such as nitrogen and phosphorus, are present in the water. Nutrients come from different sources including agriculture, wastewater, stormwater, and fossil fuel combustion. Algal blooms can cause many problems, such as deoxygenation and water toxicity, ultimately disrupting normal ecosystem functioning. In this paper, we investigate the potential impacts of climatic factors affecting water eutrophication, how these factors are projected to change in the future, and what their projected potential impacts will be

Mechanical defradation of Emplacement Drifts at Yucca Mountain- A Modeling Case Study. Part I: Nonlithophysal Rock

This paper outlines rock mechanics investigations associated with mechanical degradation of planned emplacement drifts at Yucca Mountain, which is the designated site for the proposed U.S. high-level nuclear waste repository. The factors leading to drift degradation include stresses from the overburden, stresses induced by the heat released from the emplaced waste, stresses due to seismically related ground motions, and time-dependent strength degradation. The welded tuff emplacement horizon consists of two groups of rock with distinct engineering properties: nonlithophysal units and lithophysal units, based on the relative proportion of lithophysal cavities. The term 'lithophysal' refers to hollow, bubble like cavities in volcanic rock that are surrounded by a porous rim formed by fine-grained alkali feldspar, quartz, and other minerals. Lithophysae are typically a few centimeters to a few decimeters in diameter. Part I of the paper concentrates on the generally hard, strong, and fractured nonlithophysal rock. The degradation behavior of the tunnels in the nonlithophysal rock is controlled by the occurrence of keyblocks. A statistically equivalent fracture model was generated based on extensive underground fracture mapping data from the Exploratory Studies Facility at Yucca Mountain. Three-dimensional distinct block analyses, generated with the fracture patterns randomly selected from the fracture model, were developed with the consideration of in situ, thermal, and seismic loads. In this study, field data, laboratory data, and numerical analyses are well integrated to provide a solution for the unique problem of modeling drift degradation

Evaluating The Potential of Geopolymer Concrete as A Sustainable Alternative for Thin White-Topping Pavement

Introduction: The construction industry uses a large quantity of natural materials in the production of concrete. Although attempts to incorporate green materials in concrete began years ago, not every building uses such materials today, and roadways, particularly, still rely on unsustainable materials. Methods: Therefore, this study used alternative materials, including fly ash, manufactured sand aggregates, and different molarities of alkaline activators, to incorporate waste byproducts in a geopolymer concrete white-topping pavement layer. Recent developments have led to the emergence of geopolymers as distinct classes of materials. In the 1990s, fly ash-based geopolymers became more popular than other kinds, as they are more efficient compared to Portland cement concrete. Results: Aluminosilicate gel can be obtained by combining fly ash and alkaline solution. A comprehensive literature review of geopolymer concrete was performed in this study. It examines its critical design parameters, including alkaline solutions, curing temperatures, curing methods, workability, and compressive strength under various environmental conditions. This review provides a unique opportunity for researchers to understand how geopolymer concrete performs. Discussion: A range of conditions were investigated to determine how to enhance and use this material in a variety of ways. The fresh characteristics of different mixes were studied using slump and Vee-Bee tests, and the characteristics of the cured concrete mixes were determined using flexural, compressive, and flexural fatigue tests. The results indicated that the use of manufactured sand and fly ash with high-molarity alkaline activators results in a geopolymer concrete with an excellent maximum resistance of 5.1 N/mm2 workability, strength, and fatigue properties, making it suitable for use in roadway pavement

Mechanical properties of tuffaceous rocks under triaxial conditions

Yucca Mountain has been designated as a potential site for a high level nuclear waste repository. Part of the site characterization program is an investigation of the mechanical properties of, the tuffs which comprise Yucca Mountain. This study tested specimens of TCw tuff in triaxial compression to observe the effects of confining pressure, saturation, strain rate, and anisotropy on the compressive strengths and Young`s Moduli of the specimens. Test results have shown that increasing the confining pressure increased the compressive strength and generally increased the Young`s Modulus. Saturation appears to lower both the compressive strength and Young`s Modulus of the specimens. Increasing strain rates increases the compressive strengths, but lowers the Young`s Modulus values. There appears to be a stiffness anisotropy where the specimens are stiffer perpendicular to the orientation of the lithophysal cavity orientation. Correlations with porosity have shown an increase in porosity generally lowers both the compressive strength and the Young`s Modulus of the specimens. From the triaxial tests, the Mohr -- Coulomb strength parameters have also been determined. A comparison between the strengths and modulus values from this study, values from previous studies and the suggested values reveal that the values computed for this study are generally lower than the previously published data. This discrepancy may be due to sample and specimen differences between the studies

Anisotropy of mechanical properties of tuff at Yucca Mountain

The purpose of this study is to investigate anisotropy of mechanical properties, namely, compressive strength and modulus, for Tiva Canyon welded tuff from the starter tunnel at Yucca Mountain. Mechanical properties of Tiva Canyon Tuff are needed for the design of the ramps and drifts within the Tiva Canyon horizon. Approximately one cubic foot block samples, all of which were from the thermo -- mechanical unit TCw, were obtained from a muck pile containing excavated rock from the starter tunnel. Specimens were cored from the block samples in two distinct orientations: parallel and perpendicular to the lithophysal cavity orientation. Since lithophysal cavity orientation is predominantly horizontal in the field, parallel specimens can be considered horizontal and perpendicular specimens vertical with respect to the rock mass. The specimens were NX sized (5.4 cm diameter) and had a length-to-diameter ratio of 2:1. The air dried specimens were tested at room temperature in a triaxial chamber at confining pressures of 0.1, 5, and 10 MPa, and at a compressive axial strain rate of 10{sup {minus}5} s{sup {minus}}. The Young`s Modulus values were calculated by a least squares fit of stress - strain data between 10 and 50% of the ultimate strength

Mechanical Degradation of Emplacement Drifts at Yucca Mountain-A Modeling Case Study-Part I: Nonlithophysal Rock

This paper outlines rock mechanics investigations associated with mechanical degradation of planned emplacement drifts at Yucca Mountain, which is the designated site for the proposed US high-level nuclear waste repository. The factors leading to drift degradation include stresses from the overburden, stresses induced by the heat released from the emplaced waste, stresses due to seismically related ground motions, and time-dependent strength degradation. The welded tuff emplacement horizon consists of two groups of rock with distinct engineering properties: nonlithophysal units and lithophysal units, based on the relative proportion of lithophysal cavities. The term ‘lithophysal’ refers to hollow, bubble like cavities in volcanic rock that are surrounded by a porous rim formed by fine-grained alkali feldspar, quartz, and other minerals. Lithophysae are typically a few centimeters to a few decimeters in diameter. Part I of the paper concentrates on the generally hard, strong, and fractured nonlithophysal rock. The degradation behavior of the tunnels in the nonlithophysal rock is controlled by the occurrence of keyblocks. A statistically equivalent fracture model was generated based on extensive underground fracture mapping data from the Exploratory Studies Facility at Yucca Mountain. Three-dimensional distinct block analyses, generated with the fracture patterns randomly selected from the fracture model, were developed with the consideration of in situ, thermal, and seismic loads. In this study, field data, laboratory data, and numerical analyses are well integrated to provide a solution for the unique problem of modeling drift degradation

MECHANICAL DEGRADATION OF EMPLACEMENT DRIFTS AT YUCCA MOUNTAIN - A CASE STUDY IN ROCK MECHANICS, PART 1: NONLITHOPHYSAL ROCK, PART 2: LITHOPHYSAL ROCK

This paper outlines rock mechanics investigations associated with mechanical degradation of planned emplacement drifts at Yucca Mountain, which is the designated site for a US high-level nuclear waste repository. The factors leading to drift degradation include stresses from the overburden, stresses induced by the heat released from the emplaced waste, stresses due to seismically related ground motions, and time-dependent strength degradation. The welded tuff emplacement horizon consists of two groups of rock with distinct engineering properties: nonlithophysal units and lithophysal units, based on the relative proportion of lithophysal cavities. Part I of the paper concentrates on the generally hard, strong, and fractured nonlithophysal rock. The degradation behavior of the tunnels in the nonlithophysal rock is controlled by the occurrence of keyblocks. A statistically equivalent fracture model was generated based on extensive underground fracture mapping data from the Exploratory Studies Facility at Yucca Mountain. Three-dimensional distinct block analyses, generated with the fracture patterns randomly selected from the fracture model, were developed with the consideration of in situ, thermal, seismic loads. In this study, field data, laboratory data, and numerical analyses are well integrated to provide a solution for the unique problem of modeling drift degradation throughout the regulatory period for repository performance

Measurements of Soluble Salt Content of Soils from Arid and Semi-Arid Regions

Soils with soluble salts occur in arid regions worldwide. Depending on the amount of soluble salts present, treatment of these soils may be needed before construction. In engineering, the amount present is usually determined gravimetrically by finding the weight loss for a soil diluted with a fixed quantity of water. However, if the soluble salt content is evaluated with an insufficient amount of water, some of the salt present may not dissolve. This condition, termed “salt saturation,” may cause the amount of soluble salts present to be underestimated. To identify the correct dilution, this paper proposes checking successive dilutions until an unsaturated solution is obtained. This can be accomplished using either gravimetric or electrical conductivity measurements to detect salt saturation. The volume of water used to determine percent soluble salts can then be adjusted accordingly. This paper describes how to find the most suitable dilution using either method and how to determine the percent of soluble salts. Using this approach, five different soils from Las Vegas, Nevada, were evaluated. Unsaturated water-soil dilution ratios ranged from 2:1 to 100:1. In two cases, the 2:1 dilution was adequate, but for the other three it was not. Soil “M” exemplified this best: percent soluble salts increased from 1% measured at a 5:1 dilution (indicating a leave-in-place/no-action recommendation) to 7% at a 100:1 dilution (indicating a removal recommendation). This result illustrates the importance of using an unsaturated dilution for determining percent soluble soil